Tamper respondent sensors are utilized in various applications, including the transport of sensitive information and protecting electronic devices. Typical sensors are in the form of envelopes and shallow boxes, the walls of which are formed by folding flexible sheets incorporating tamper detection features. Included in such sensors are layers of flexible material including a matrix of conductive or semi-conductive lines printed on thin insulating film. The matrix of lines forms a continuous conductor which is broken if attempts are made to penetrate the film. The circuit is monitored by opening the conductor at one point and measuring the resistance between the two ends of the circuit. The resistance changes if the circuit is broken, for example because of tampering.
Typically, the sensors are wrapped around the outside of the device to be protected. In many applications, however, the device to be protected is also required to have some form of external ruggedization around it. That is, many electronic devices have an external box or casing that provides strength for transportation or in use. Accordingly, some form of internal tamper respondent sensor is desired.